Retaining walls tp support cut in solid rock 1

[aayjaber]

I am in the process of planning a 100 ft long retaining wall to support grading for a new house of a sloped up lot. The height of the retaining wall ranges from 5 to 8 ft. The area is labeled as seismic and geo-hazard as most of San Jose CA is. I am doing some exploratory digging on the land mainly for landscaping purposes and in some area I have to cut into the hill side to create flat terraces for the trees I am growing, this is giving me a great opportunity to learn about the geology of the land. Here are my observations:

1- Top soil is only 1 ft with plus or minus in some area.
2- After the top soil is cleared I reach solid bedrock which I can describe as continuous, by most by the time you reach 2 feet depth you are on a continuous solid bedrock.
3- The make up of the bedrock is very solid stones raning in size from small to huge all connected together by less solid material but very stable and require very hard chizzling or even power tools like a compressor with hammering jack to remove.
4- When you cut in the bedrock you expose a very stable cliff that in my opinion as strong as concrete. I thought I would like to keep this exposed since the colors of the stones exposed makes the look and feel a great thing and I believe the cliff is extremely stable and will never move.

What will I need to do to convince the city that I do not need a structural retaining so I can keep my view on the natural as exposed by the cut?

Many thanks

Aad

 

[msquared48]

Hire a local geotech that could advise you and the City on the pros and cons of your thinking.

Mike McCann
McCann Engineering

 

[msucog]

if that were here, rock coring would likely be required to evaluate the bedding, fractures, strength, etc relative to what is planned. the geotech would need to perform the exploration and evaluate the stability of such a wall for your locale. the house foundation location and loads relative to the wall will likley be a critical detail that the geotech will need to know (sure would hate to see the house end up like other houses i've seen on the nightly news where they fall off the side of a hill).

 

[cvg]

you say you have observed the geology, however no mention of:
a) type of rock / geologic units
b) quality of the rock (except for "strong as concrete")
c) location of any faults
d) bedding conditions
e) strike and dip
f) surficial topography

without an adequate investigation of the geology, there can be no reasonable conclusion drawn on the stability of your cliff. you need a geologist

 

[muuddfun]

definitely get a geologist to map it for you, the city likely shouldn't accept anything without the mapping.

One thing you could do is to make a false cut 10 or 15 feet off of the proposed final edge and see what you have, get the geologist to map it, do some slope stability calcs etc., then cut it to final design if it is ok. We have proposed to do that were there are questions about the geology, and you can't find everything with borings.

 

[theCorkster]

Get a certified engineering geologist (CEG) familiar with the area geology to first review the site with respect to the area geology. You're dealing with the geology of the terrances acreted to the California coast, and in many cases, what appears stable is not.

Since you are cutting into slopes, although the cuts are relatively small, the potential impacts upslope should be well understood. Let the CEG develop a scope of work to answer your questions. It will go through your building official with more ease, and may save a lot of grief later on!